Scoparia dulcis (PROSEA)

Plant Resources of South-East Asia
Introduction

Protologue: Sp. pl. 1: 116 (1753).

Family: Scrophulariaceae

Chromosome number: 2n= (20), 40

Scoparia dulcis L. - 1, flowering and fruiting branch; 2, lateral view of flower; 3, top view of flower; 4, fruit; 5, seed

Synonyms

Scoparia ternata Forssk. (1775),
Gratiola micrantha Nutt. (1822),
Scoparia grandiflora Nash (1896).

Vernacular names

Sweet broomweed, Macao tea (En).
Herbe à balai, balai doux (Fr)
Indonesia: ginje menir, ginje jepun (Javanese), jakatuwa (Sundanese)
Malaysia: teh makao, cha padang, pokok delis
Philippines: mala-anis, sampalokan (Tagalog), isisa (Iloko)
Thailand: mafai duean ha (Bangkok), kratai chaam yai (south-eastern), yaa hua maeng hun (northern)
Vietnam: cam thảo nam, dã cam thảo, cam thảo dất.

Origin and geographic distribution

S. dulcis is native of tropical America, but has long since become a pantropical weed. It is widely distributed in South-East Asia, India and China.

Uses

S. dulcis roots, leaves and tops are traditionally used in India, Indo-China and South-East Asia as an analgesic, diuretic and antipyretic, to treat gastric disorders such as diarrhoea and dysentery, and also for cough, bronchitis, hypertension, haemorrhoids and insect bites. In Malaysia and India, the leaves are chewed to treat cough; they first taste bitter and later sweet (like licorice). In Vietnam, the whole plant is also used for treating snakebites and as an antidote for cassava intoxication. The fresh or dried plants are used to treat pimples, impetigo, ulcers and eczema. In India, a decoction of the plant is drunk for gonorrhoea and to induce labour, and the leaves were formerly used in the treatment of diabetes. A cold decoction of the plant is taken for gravel and kidney complaints. An infusion of the seeds obtained by soaking them in water overnight is a cooling drink. The Chinese also use the whole plant against herpes. In India and Burma (Myanmar), an infusion of the herb is used as a mouthwash for infected gums.

In West Africa and South America, S. dulcis is also extensively used as a medicinal, basically in the same way as in India. In Sierra Leone, an infusion of the plant is taken for remittent fever and gonorrhoea. For feverish headache, the leaves or the whole plant are macerated in warm water and drunk copiously when cooled. In Liberia, a decoction is taken cold for gravel and kidney complaints. A decoction is applied as a fomentation to bruises and contusions. In Trinidad, a decoction of the plant is taken as a remedy for diabetes, urinary burning, diarrhoea and eczema. An infusion is used to bathe children suffering from rash, sores or marasmus, while the juice of the leaves is given for jaundice and as an anodyne eyewash. In Mexico, the astringent, mucilaginous decoction is commonly applied to bruises and contusions. The fresh or dried plants are said to kill fleas, lice and intestinal worms.

In Indonesia, the leaves were formerly used as a substitute for opium. The leaves are smoked in Gabon, in place of tobacco. In South America, S. dulcis is sometimes planted as a sand-binder. In India and Brazil, the plant is used as cattle fodder.

Production and international trade

S. dulcis is traded on local markets in Asia and Africa, as a medicinal. No data on trade statistics are available.

Properties

Aerial parts of S. dulcis contain about 4% of a viscous oil, which besides fatty acids like stearic, myristic and linolenic acid contains a series of diterpenes e.g. dulciol, scoparol, scopadulcic acid A and B, scopadulciol, scoparinol, dulcinol and dulcilone. They also yield nitrogen-containing components such as 2-hydroxy-2H-1,4-benzoxazin-3-one and 6-methoxy-benzoxazolinone (from the roots). The aerial parts also contain flavonoids including acacetin, apigenin and circimarin.

Analysis of the diterpene composition of S. dulcis from different sources (Taiwan, China, Thailand, Paraguay), revealed the presence of 2 chemotypes based on the major components: the SDX type, which produces scopadulciol and scopadiol, and the SDB type, which produces scopadulcic acid B and scoparic acid A. The hereditary nature of these phenotypes was confirmed by analysis of the progeny of the chemotypes. Furthermore, callus and multiple shoots derived from an SDX-type produced scopadulciol. Similar amounts of scopadulciol were produced by multiple shoots and callus cultures (5-fold higher than that produced by SDB-type multiple shoots).

Several of the isolated diterpenes have pharmacological activity, e.g. scopadulin, an aphidicolane-type diterpene from the aerial parts, which showed mild antiviral activity. Its cytotoxicity (ID₅₀) against HeLa cells was 285 μg/ml and its inhibitory activity (ED₅₀) against herpes simplex virus type 1 (HSV-1) was 38 μg/ml. The antiviral activity of scopadulciol (SDC), a tetracyclic diterpenoid related to aphidicolin, was also studied in vitro against herpes simplex virus type 1 (HSV-1). SDC was found to inhibit the virus replication, as shown by reduction of virus production. The action was not due to the inhibition of viral DNA polymerase activity or virus penetration, but might involve a virucidal effect.

Scopadulcic acid B (SDB), a tetracyclic diterpenoid, inhibited the effects of tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) in vitro and in vivo. SDB inhibited TPA-enhanced phospholipid synthesis in cultured cells, and also suppressed the promoting effect of TPA on skin tumour formation in mice initiated with 7,12-dimethylbenz(a)anthracene. The potency of SDB proved to be stronger than that of other natural antitumour-promoting terpenoids, such as glycyrrhetinic acid. In addition, SDB has also been shown to inhibit replication of herpes simplex virus type 1 (HSV-1) and the enzyme H⁺,K⁺-ATPase from the gastric mucosa.

In addition, the fresh stems and leaves of S. dulcis contain a compound called amellin, thought by some to have an important therapeutic action in diabetes; however, others doubt this. Oral administration of amellin relieves symptoms of glycosuria, reduces hyperglycaemia and increases RBC count. It has also been found helpful in anaemia, albuminuria, ketonuria, retinitis and other complications associated with diabetes mellitus. Unlike insulin, amellin does not cause blood sugar levels to drop below normal and reduction of both blood and urine sugar occurs gradually.

The aqueous and ethanol extracts from the aerial parts were found to be active in the carrageenin induced rat paw oedema model, at 0.5 and 1 g/kg, p.o. (at 40% and 70%, respectively), and also inhibited the exudate and leukocyte migration induced in the rat pleurisy model (by 60% and 70%, respectively). Both extracts reduced acetic acid induced writhing in mice (20-60%), but were ineffective in the tail flick test. The sympathomimetic activity of an ethanol extract was also evaluated in rodent preparations in vivo and in vitro. Administration of this extract to anaesthetized rats produced a dose-related hypertension blocked by theα-adrenoceptor antagonist prazosin. Partition of the extract in chloroform-water yielded an aqueous phase 20 times more potent than the extract; this produced hypertension in either reserpine-treated or pithed rats. Prazosin reduced the maximum contractile effect of the aqueous fraction, and shifted the concentration-response curves for noradrenaline to the right. The aqueous fraction increased the inotropism of electrically driven left atria of rats, the effect being blocked by propranolol. In preparations of guinea-pig tracheal rings the aqueous fraction relaxed the muscle contraction induced by histamine in proportion to the concentration. The effect was antagonized competitively by propranolol. The results indicated that both catecholamines may account for the hypertensive and inotropic effects obtained after parenteral administration of the extracts. This sympathomimetic activity is, however, unrelated to the previously reported analgesic and anti-inflammatory properties of the plant extract, but may explain its effectiveness as a topical application in the healing of mucosal and skin wounds.

Finally, in a clinical trial 25 healthy people and 30 with gingivitis were given mouthwashes containing 1% aqueous extract or 0.02% chlorhexidine gluconate for 6 weeks. There was a slight increase in gingival inflammation in people with gingivitis using the extract, but the antiplaque activity was similar to that of 0.02% chlorhexidine.

Description

An annual to perennial, erect, much branched herb, 20-75 cm tall, glabrous, 4-6-striate.
Leaves opposite or 3-4-whorled, oblanceolate to oblong-obovate, 0.5-3.5 cm × 0.2-1.5 cm, base attenuate, apex acute, margin coarsely acute-serrate, glabrous above, gland-dotted beneath; petiole 0.5-1 cm long; stipules absent.
Flowers axillary, bisexual, actinomorphic, 1-4-fascicled, regular, pedicel 3-7 mm long; calyx deeply 4-lobed, 2 mm long, accrescent in fruit to 2.5 mm, lobes oblong-ovate, subacute; corolla rotate, white or very pale-purple, sometimes with darker centre, deeply 4-lobed, lobes oblong, 3 mm long, apex obtuse, throat on inside with dense, long white hairs; stamens 4, subequal, erect, filaments filiform, 2 mm long; ovary superior, 2-celled, glabrous, style filiform, 1.5 mm long, stigma capitate.
Fruit a subglobose capsule, 2.5-3 mm long, 4-valved, thin-walled, yellowish-brown, seeds numerous.
Seed oblong-globose to ovoid, 0.5-0.6 mm × 0.3-0.4 mm, angular, covered with thin, reticulate testa, brown.
Seedling with epigeal germination; cotyledons rhomboid, up to 2.2 mm long, glabrous, petiolate, epicotyl 1.5-4 mm long, 4-angular; first leaves 2, ovate, up to 6 mm long, glandular dotted, margin with rounded teeth, midvein present, petiolate.

Growth and development

S. dulcis is found flowering and fruiting throughout the year.

Other botanical information

Scoparia consists of about 20 species, originating from tropical America. Some Scoparia have become pantropical weeds.

Ecology

S. dulcis is a common weed on waste ground, along roads, in dry deciduous forest and dry rice fields, from sea-level up to 700 m altitude. It prefers regions ranging from everwet conditions to a prolonged dry season, and grows on all kinds of soils.

Propagation and planting

S. dulcis is propagated by seed, and can produce 800-1000 seeds per plant. Light was found to be the primary environmental factor affecting seed germination; full germination required 32 h continuous light, 3 days of 8 h light/day or 4 days of 4 h light/day. Temperature had no effect on the final germination rate, but it affected the speed of germination. At 15°C, the start of germination was delayed by about 3 days for imbibed seeds and 5-6 days for dry seeds, when compared with germination at 23-31°C.

In vitro production of active compounds

Production of scopadulcic acid B and scopadulciol by leaf organ culture was examined by addition of cytokinins to culture media. Of the tested cytokinins, N-phenyl-N'-(4-pyridyl)urea was the most efficient when added to the mass spectroscopic liquid culture medium at 0.1μM. 6-Methoxybenzoxazolinone (MBOA) was found to be present in all plant parts, with the highest concentration being observed in younger leaves. The content of MBOA in leaves increased with the growth of the plant before the fruiting stage. MBOA was also found to be produced by the callus tissues, multiple shoots and hairy roots.

Diseases and pests

In Togo, S. dulcis was found to be a probable host for the coconut-yellows-disease, caused by a mycoplasma-like organism.

Harvesting

In Vietnam, S. dulcis is harvested during the rainy season.

Handling after harvest

In Vietnam, whole plants of S. dulcis are thoroughly washed before drying in the sun or in an oven.

Genetic resources and breeding

S. dulcis is widespread and common throughout South-East Asia, and there is no danger of genetic erosion. As several chemotypes exist in S. dulcis throughout the world, it is important to get a clear view of these different types, for possible breeding purposes.

Transgenic herbicide-resistant plants were obtained through Agrobacterium-mediated transformation by means of scratching young plants. Hairy roots resistant to the herbicide bialaphos were selected and plantlets were regenerated. Transgenic plants accumulated scopadulcic acid B, a specific secondary metabolite of S. dulcis, in amounts of 15-60% of that in normal plants. The transgenic plants and progenies showed resistance to the herbicides bialaphos and phosphinothricin.

Prospects

In general, diterpenes possess a wide range of pharmacological activities. This is also true for S. dulcis: e.g. antiviral, antitumour and enzyme inhibition. However, diterpenes are also known for their often strong (cyto-)toxicity. Therefore, more research of the isolated compounds and extracts is necessary to fully evaluate a future potential.

Literature

Hayashi, T., Kasahara, K. & Sankawa, U., 1997. Efficient production of biologically active diterpenoids by leaf organ culture of Scoparia dulcis. Phytochemistry 46(3): 517-520.
Hayashi, T., Kawasaki, M., Miwa, Y., Taga, T. & Morita, N., 1990. Antiviral agents of plant origin. III. Scopadulin, a novel tetracyclic diterpene from Scoparia dulcis. Chemical and Pharmaceutical Bulletin 38(4): 945-947.
Hayashi, T., Okamura, K., Kawasaki, M. & Morita, N., 1991. Two chemotypes of Scoparia dulcis in Paraguay. Phytochemistry 30(11): 3617-–3620.
Morton, J.F., 1981. Atlas of medicinal plants of Middle America. Bahamas to Yucatan. Charles C. Thomas, Springfield, Illinois, United States. pp. 815-–816.
Nishino, H., Hayashi, T., Arisawa, M., Satomi, Y. & Iwashima, A., 1993. Antitumor-promotor activity of scopadulcic acid B isolated from the medicinal plant Scoparia dulcis L. Oncology (Basel) 50(2): 100-103.
Quisumbing, E., 1978. Medicinal plants of the Philippines. Katha Publishing Co., Quezon City, the Philippines. pp. 872-873.

Other selected sources

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Authors

N.O. Aguilar & G.H. Schmelzer